Heat the olive oil in a large skillet or grill pan over high heat and add the onions and peppers. Cook the vegetables for about two minutes until slightly tender and very fragrant. Add the garlic, the corn, black beans, lime juice and seasonings and cook for another 4 minutes or so until fragrant and tender, but still slightly crisp.
Heat a large non-stick skillet over medium heat. Butter one side of each slice of bread. Place two slices, butter side down in the pan. Top with a slice of cheese, a generous helping of the filling, top with more cheese, and another slice of bread, butter side up. Cook for about 3 minutes on the first side until the bread has browned and the cheese begins to melt. Flip and cook an additional 3-4 minutes until the cheese is melted and the outside of the bread is toasted. Remove from the pan. Repeat with the remaining bread and filling and serve hot.